1. Field of the Invention
The present invention relates generally to a coating method and apparatus, and more particularly to a coating method and apparatus for coating a continuously-traveling web with coating liquids flowing down a slide surface of a coating hopper in manufacturing photographic film, photographic printing paper, magnetic recording tape, adhesive tape, pressure sensitive paper, offset printing plates, batteries, and so forth.
2. Description of Related Art
A slide bead coating apparatus is an example of coating apparatuses for applying coating liquids on the surface of a continuously-traveling web. U.S. Pat. No. 2,761,791 of Russell discloses a multilayer slide bead coating apparatus. According to this apparatus, a plurality of coating liquids flowing down a slide surface form beads in a gap where the coating liquids meet the traveling web, and the coating liquids are applied to the surface of the web through the beads.
There is also a curtain coating apparatus that coats the surface of the web with coating liquids through laminar flows thereof, which are formed between a lip and the traveling web.
The above-mentioned coating apparatuses must regulate the width of the coating liquids flowing down the slide surface in order to coat the webs with different widths.
For example, Japanese Patent Provisional Publication No. 57-110364 discloses a coating apparatus that regulates the width of the coating liquids to a desired width with guide plates. This apparatus is provided with a pair of the guide plates on the slide surface at both sides in the width direction of the slide surface, and the guide plates extend from the base end to the front end of the slide surface. The pair of guide plates regulate the width of the coating liquid.
This conventional coating apparatus, however, must be stopped every time there is a change in the web width, and coating hoppers must be changed according to the web widths.
To regulate the width of the coating liquids without changing the coating hoppers in a conventional coating apparatus shown in FIG. 11, the positions of the guide plates 103, which are provided on the slide surface 102, are changed so that the width of the coating liquids is regulated to a desired width W.sub.2 in conformity with the web width. In addition, pocket stoppers 106 and spacers 107 must be inserted into manifolds 104 and slits 105, respectively, so that both ends of the manifolds 104 and the slits 105 are positioned at both ends of the desired width W.sub.2.
Moreover, since there are changes in the capacities of the manifolds 104 and the slits 105 resulting from the insertion of the pocket stoppers 106 and the spacers 107, it is necessary to change the amount of the coating liquids supplied to the manifolds 104 according to the capacity in order to achieve a desired coating amount.
Hence, a time loss resulting from the stop in the coating operation, the changes in conditions, etc. significantly lowers the working efficiency, and it is necessary to provide the coating hoppers 101, the pocket stoppers 106, the spacers 107, etc. in the same number as the widths of the webs.
Furthermore, the above-mentioned coating apparatuses cannot coat the web satisfactorily if the web takes a winding course, because the guide plates 103 are fixed. To apply the coating liquids on the web that is taking a winding course in the conventional coating apparatus, there is no other way but to use an excessively wide web to leave uncoated areas with proper widths at both edge regions of the web. The edge regions of the web must be cut off after the coating, which drops the yield.